Metal working method and lubricant



July 1954 R. H. DALTON ETAL 3,140,779

METAL WORKING METHOD AND LUBRICANT Filed Aug. 6, 1962 2 Sheets-Sheet l 7Z=M m9 7052 35619555 F o O I O o O .l o o o o 8 8 8 g Q Q o a 9 INVENTORS 8 2 88 m (u w m fiaeE/e'rA Aura/v h ;s-/0 lv/ xz/yoasvj mean" BY M fag;

July 14, 1964 R, H DALTON ETAL 3,140,779

METAL- WORKING METHOD AND LUBRICANT Filed Aug. 6, 1962 2 Sheets-Sheet 2 INVENTORS P055197 if D/u ra/v working.

United States Patent Ofilicc 3,140,779 Patented July 14, 1964 3,140,779 METAL WOEHGNG METHOD AND LUbREQANT Robert H. Dalton, Corning, NY and William H. Kroeclr, Bethlehem, Pa, assignors to Corning Glass Works, Corning, Nil! a corporation of New York Filed Aug. 6, 1962, Ser. No. 2163317 6 Claims. (Cl. 207--1tl) This application is a continuation-in-part of our prior application Serial No. 529,280, filed August 18, 1955, now abandoned, and Serial No. 188,301, filed April 12, 1962, now abandoned.

This invention relates in general to the art of metal working and is more particularly concerned with the lubrication of die members used in that art.

It has recently been proposed to employ vitreous lubricating agents, particularly glasses and enamels, in hot metal working operations such as extrusion or forging of metal workpieces. In general, such operations involve bringing a preheated workpiece into contact with the lubricated shaping surface of a die member and subjecting the workpiece to relatively high shaping pressures whereby it is extruded, forged, or otherwise conformed to the shape of the particular die involved.

Operations of this nature are of necessity conducted at relatively high temperatures. Thus, operating temperatures may vary from about 1500 F. or less for bronze metals up to around 2500 F. for certain steels and even higher temperatures for more refractory metals such as molybdenum or titanium.

Organic type lubricants are generally ineffective at these elevated temperatures and inorganic salts find little use because of their high fluidity or low viscosity in the molten state. Vitreous materials on the other hand have a high viscosity in the molten state and like organic lubricants, become progressively softer or less viscous with increasing temperatures. Further, such softening occurs at the elevated temperatures required for metal Also vitreous materials do not undergo chemical change, such as oxidation or decomposition, at these temperatures.

In operating at the relatively high temperatures involved it is quite desirable to have a relatively large temperature range within which to work. Among the reasons for such a working range are variations in metal preheating conditions and in the amount of heat loss during transfer of the metal and during actual shaping operations. Narrowing of the working range involves increasingly expensive and time-consurning means of tures in which case the lubricant becomes so thin that it is forced off the die surface or, conversely, by decreasing temperatureswith the lubricant becoming so stiff as to require an undue amount of pressure on the metal being shaped.

It is generally understood that a vitreous material is effective for metal working lubrication within a viscosity range of 10 to 1000 poises, preferably 100 to 500 poises. Accordingly, the viscosity-temperature characteristics of a lubricant essentially define the elfective working range for a metal with such lubricant. It is therefore desirable to match metals and lubricants in this respect, and especially important to provide as broad a range of temperatures for metal working as possible. To this end, a vitreous lubricant should have a flat viscosity curve, that is a broad temperature range, corresponding to the effective range of viscosities for metal working.

Generally speaking, previously known vitreous lubrieating materials have been characterized by relatively rapid changes in viscosity with temperature, that is high viscosity gradients, or steep curves within the indicated working range. As a result, prior glass lubricants have often imposed on metal-working operations a considerably narrower temperature range than desired.

In using vitreous lubricants, the material is usually applied to the die surface prior to the start of metal working operations, although it may also be applied to the contacting surface of the metal being worked. It may be applied as an adherent coating or in the form of a thin plate, disc, fibrous mat or powdered layer. As the preheated metal workpiece contacts the vitreous material, at least the portion of the vitreous material contacted is fused or softened, and forms a thin lubricating film between the metal workpiece and the die. At the conclusion of the metal working operation the shaped metal article, when cooled, has a thin film of solid lubricant over its surface which must be removed. Heretofore, removal of such film has presented somewhat of a problem. While it may be physically removed by cracking or chipping, such procedure is tedious and may result in serious damage to the metal surface. Likewise, chemical removal, as by said etching, is both expensive and inconvenient to carry out, particularly on relatively large surfaces.

It is the purpose of the present invention then to provide improvements in metal working methods characterized by the use of vitreous lubricants, which substantially avoid the prior deficiencies noted above, such improvements being particularly concerned with the lubricants used. The invention is based on the discovery that fused boric oxide, and boric oxide-silica mixtures, produce a family of glass compositions which have a low viscosity gradient, that is, undergo a relatively small change of viscosity with change in temperature, particularly at viscosities suitable for metal working, and further that such glasses are easily and readily dissolved in water.

Accordingly, our invention involves vitreous metalworking lubricants and a method of shaping, at elevated temperatures and under pressure, a metal workpiece against a die member having at its shaping surface as a vitreous lubricant a glass consisting of 50-100% B203 and Fused B 0 functions satisfactorily as a lubricant for some of the softer bronzes. However, it becomes too soft or fluid at the higher temperatures required for working of most metals including the ferrous metals. Introduction of progressively increasing amounts of SiO;;, has been found to correspondingly increase the glass viscosity at a given temperature without appreciably affecting the low viscosity gradient which characterizes fused B 0 Accordingly, SiO may be present in amounts up to about 50% depending on the metal working temperature involved, larger amounts being required for refractory metals such as molybdenum or tungsten and intermediate amounts of 2040% being adequate for most ferrous metals. Advantageously, however, the SiO content is maintained as low as possible for any given metal since there is a tendency for the water solubility of the glasses to decrease with increasing amounts of SiO The present lubricating glasses should consist entirely of 50100% B 0 and 0-50% SiO Other compatible materials commonly used in glassmaking, such as the oxides of the alkali metals, the alkaline earth metals and aluminum, undesirably alter such properties of the glass as water solubility and viscosity gradient and should be avoided.

In the accompanying drawing, to which reference is made for a clearer understanding of the invention,

FIG. 1 is a graph illustrating the viscosity-temperature characteristics of various glasses.

FIG. 2 shows a partial longitudinal vertical section of an extrusion press during extrusion of a solid bar in accordance with the present invention.

In the graph of FIG. 1 viscosity in poises is plotted against temperature in degrees F. and curves are drawn showing the characteristics of six different glasses. Four of the curves, identified by the indicia X-1 to X-4 are based on data obtained from a series of glasses embodied in and illustrating the present invention. The compositions of these glasses are set forth in percent by weight in Table I below, the identifying indicia of the glasses corresponding to that of the curves. Also set forth is the average viscosity gradient or slope T/ V in C./poise as calculated from each corresponding curve over the vis- The remaining two curves, designated A and B and included for comparative purposes, are based on glasses typical of those heretofore proposed for, or used as, lubrications on metal-shaping dies. Glass A is a soft, lead borate type glass such as used for lower temperature work, while glass B is a soda-lime-silicate type glass used in higher temperature Work such as extrusion of certain steels. Respectively, these glasses have corresponding T/ V values of 0.6 and 12 C./poise.

Only viscosities between and 1000 poises are included on the graph since this is the range generally considered useful for present purposes. It may be noted that above 1000 poises all of the glass viscosities continue to rise more rapidly with temperature decrease, as the curves indicate and in line with conventional glass viscosity gradicuts.

An inspection of the viscosity curves in FIG. 1 readily reveals the marked difference in the viscosity characteristics of our present glasses and those previously used. The present glasses are variously described as having a flat viscosity curve or as having a low viscosity gradient expressed as a T V value of about 1.8. From a practical standpoint the resulting working range is the significant factor. If the 100-500 poise range, often thought to be optimum for lubrication, be considered, it will be seen that glasses A and B have working ranges of about 140 F. and 300 F., respectively. Glasses X-l and X4 of the present invention on the other hand have working ranges of 460 F. to 560 F. within the same viscosity range. This means a two to four fold increase in breadth of working range with the present glasses.

The manner in which progressively increasing amounts of SiO progressively increase the viscosity at any given temperature will also be noted. The present family of glasses, taken in its entirety, provides a family of viscosity curves (similar to those illustratively shown) which permit selection of a suitable glass composition once viscosity range and operating temperatures are established.

The characteristic solubility of the present glasses in water is demonstrated by a simplified version of a conventional durability or weathering test. Glass bodies, formed from the various glasses X-l to X4 and approximately 1 cubic centimeter in volume (about 2.3 grams in weight), were immersed in boiling water. Each of the glass bodies was completely dissolved within 8 to 10 minutes. Under similar test conditions glass bodies formed from glasses A and B, the prior art glasses referred to above, were reduced in weight by an almost negligible amount, about 0.42 milligram of glass A being dissolved and only about 0.002 milligram of glass B, a relatively stable commercial glass.

In FIG. 2 the present invention is illustratively shown as applied to a typical metal working process, namely extrusion of a preheated metal billet. In setting up such process an extrusion chamber 11 is fitted with a die member 12 having a die opening 13 through which a preheated metal billet 14 is extruded in the form of a rod 15 by the pressure of plunger 16. Prior to introducing billet 15 into extrusion chamber 11 a layer of lubricating glass 17 is positioned in contact with the ledge or face 18 of die member 12. As billet 14 is brought into contact with glass 17 and pressure applied through plunger 16 the surface portion of glass 17 is melted and forms a thin lubricating film 19 over rod 15 as such rod is extruded through die opening 13. As the extrusion continues glass 17 continues to melt and provide a continuous supply of lubricant.

Alternatively lubricating glass 17 may in some instances be applied to the heated billet 15, rather than the die member, as by rolling the heated billet 15 in powdered glass or dipping it in a molten glass bath.

With completion of the extrusion process extruded rod 15 cools down and lubricating layer 19 solidifies as a vitreous layer or coating over the metal surface. With the present water-soluble glasses, such solidified lubricant layer can readily be Washed off, dissolved in a water bath, or otherwise removed with water in any convenient manner. While the present lubricants can be easily removed with water alone, it will be appreciated that other aqueous type solvents such as dilute solutions of acid or alkali may be used to further facilitate the process where slight surface attack on the metal is either unimportant or is necessary to remove a scale or oxide layer.

What is claimed is:

1. In the art of shaping a body of metal by subjecting it to pressure while the body is maintained within a range of elevated temperatures and is disposed in working relationship to a die member provided with a vitreous lubricant, the method of broadening the range of metal working temperatures which comprises providing as the lubricant a glass consisting of 50100% B 0 and 040% SiO and characterized by a viscosity gradient of about 1.8 in the metal working temperature range.

2. A method of shaping a metal workpiece, by subjecting it to pressure while maintained within a range of elevated temperatures and disposed in working relationship to a die member, which comprises lubricating the die member with a vitreous material consisting of 50100% B 0 and 0-50% SiO and having a viscosity gradient of about 1.8 within the metal working temperature range.

3. A method in accordance with claim 2 wherein a film of lubricant solidifies on the shaped metal and is dissolved with aqueous solvent.

4. A method in accordance with claim 2 wherein the die member is lubricated with a vitreous material consisting of B 0 5. A method in accordance with claim 2 wherein the die member is lubricated with a vitreous material consisting of B 0 and SiO the Si0 being present in an amount sumcient to increase the viscosity of the vitreous lubricant with respect to the viscosity of vitreous boric oxide at a given temperature.

6. A vitreous lubricant, adapted to use in the shaping of a metal body within a range of elevated temperatures, which consists of 50100% B 0 and 0-50% SiO and has a viscosity gradient of about 1.8 within the metal working temperature range, the SiO being present in an amount suificient to increase the viscosity of the vitreous lubricant with respect to that of vitreous boric oxide at a given temperature.

References Cited in the tile of this patent UNITED STATES PATENTS 2,538,917 Sejournet et al. Jan. 23, 1951 2,715,765 Brown Aug. 23, 1955 2,962,808 Cole et al. Dec. 6, 1960 

1. IN THE ART OF SHAPING A BODY OF METAL BY SUBJECTING IT TO PRESSURE WHILE THE BODY IS MAINTAINED WITHIN A RANGE OF ELEVATED TEMPERATURES AND IS DISPOSED IN WORKING RELATIONSHIP TO A DIE MEMBER PROVIDED WITH A VITREOUS LUBRICANT, THE METHOD OF BROADENING THE RANGE OT METAL WORKING TEMPERATURES WHICH COMPRISES PROVIDING AS THE LUBRICANT A GLASS CONSISTING OF 50-100% B2O3 AND 3-50% SIO2, AND CHARACTERIZED BY A VISCOSITY GRADIENT OF ABOUT 1.8 IN THE METAL WORKING TEMPERATURE RANGE. 